What is the best workflow to import entire complex scenes from Cinema 4D to blender?
FBX or Alembic will provide you with similar level of support - Static geometry import is the only thing that will be fully OK.

Animation would be supported on a rather simple and limited level (for FBX, objects and rigs animations, and shapekeys; Alembic features a fully baked animation on both object and geometry levels).

Shading support would at best be very basic (FBX supports basic shading/texturing, similar to fixed pipeline of old OpenGL e.g., afaik Alembic does not handle shaders at all?).

More scene-level things (like world) would be totally lost.

So in a word, think you should either wait for Cycles to be supported by C4D, or use whatever renderer you have currently with C4D.

A complete accurate scene export between 3D apps is (and probably will remain) pretty much impossible, unless you have the means to develop your own tools (as big studios do for their own production pipeline) - and even then, they usually only convert a subset of data betweens their apps…